This invention relates to a bone nail and a targeting device for locating cross-locking holes in the bone nail.
Locking nails to care for fractures in cylindrical hollow bones are widely used. Their utilization is described, for example, in “The Journal of Trauma” of 1993, Vol. 35, No. 5, pp. 772 to 775. It is the typical of such locking nails that two cross-bores are disposed at the distal end and at least one cross-bore is disposed at the proximal end. Bone screws are passed through the cross-bores. They are screwed into the corticalis at opposed sides. This secures the locking nail axially and against a rotation.
A problem in employing such locking nails is how to identify the position of the cross-bores to drill a hole in the corticalis in the right place from outside. A number of aim-taking apparatus has become known, which work with X-rays to identify the position of the cross-bores relative to an aiming or targeting apparatus. Therefore, it is possible to drill a hole in the bone in the right place by means of the targeting apparatus and a so-called drilling sleeve or targeting sleeve. In most cases of the known targeting instruments are firmly connected to the proximal end of the nail. Such an instrument is shown in U.S. Pat. Nos. 5,176,681 and 5,454,813. Thus, the position of the cross-bores may already be preset in an approximately precise way. However, it should be considered that the presumed position of the cross-bores does not coincide with the real one because of the curvature of the bone and the possible torsion of the nail while it is driven in.
Although the position of the cross-bores may be determined by means of X-rays in a relatively precise way using X-rays is not always the best means of choice because it could cause harm to both the patient and surgeon. Therefore, it has also become known to employ targeting apparatus not including X-raying equipment. As mentioned earlier the approximate position of the cross-bores already results from the distance at which the holes are spaced from the proximal end and the circumferential position results from given markings at the proximal end of the locking nail, which cause the targeting apparatus to be connected to the nail in a given rotational position. As explained earlier, however, it is impossible to precisely identify the position of the cross-bores only in a mechanical way by using the known means.